A form of eavesdropping in which special equipment is used to pick up telecommunication signals or data within a computer device by monitoring and picking up the electromagnetic fields (EM fields) that are produced by the signals or movement of the data.
Van Eck phreaking is a form of eavesdropping in which special equipment is used to pick up side-band electromagnetic emissions from electronics devices that correlate to hidden signals or data for the purpose of recreating these signals or data in order to spy on the electronic device. Side-band electromagnetic radiation emissions are present in and, with the proper equipment, can be captured from keyboards, computer displays, printers, and other electronic devices.
source Van Eck phreaking:
